The invention relates to apparatus for measuring the position of an elongated light source inside a lighthouse used in the manufacture of luminiscent or phosphor screens of color picture tubes.
U.S. Pat. No. 3,482,495 shows apparatus for measuring the position of an exposure lamp inside a lighthouse. Lighthouses are used to expose the phosphor layer from which the screens of color picture tubes are made. The conventional lighthouse comprises a point-shaped light source with a collimator disposed thereabove. The measuring (alignment) apparatus comprises a base plate provided with stop faces (position stops) with the aid of which it is brought into alignment with a lighthouse when placed thereon. The base plate has mounted thereunder eight optical projection devices (light transmitting systems) each comprising two adjustable mirrors and one biconvex lens which image the exposure lamp on a screen disposed in the center of the base plate. The screen is subdivided into nine squares of which the outer eight ones have cross shaped targets which are illuminated by eight optical projection (light transmitting) systems. For calibration, the measuring (alignment) apparatus is placed onto a standard lighthouse. Thereafter, the eight optical projection (light transmitting) systems are adjusted in such a way that the eight squares are illuminated in their centers. Thereafter, the thus calibrated alignment apparatus is placed onto a production lighthouse, with the exposure lamp and the position stops thereof being so adjusted that again the eight squares are illuminated in their centers.